SEPARABLE PEDICLE SCREW
Techniques are generally described related to a method and system for treating an injury with a bone screw. One example bone screw may be configured to fracture at a pre-selected frangible location so that the point of failure is not in an inaccessible location, e.g., deeply embedded below the surface of a treated bone. The bone screw may further include a material disposed over the frangible location that is designed to temporarily strengthen the screw and selected to be absorbed by the body over a period of time after installation of the screw in the bone. One example bone screw may include an unthreaded portion that is configured to facilitate removal of an embedded screw fragment from a bone in the event that the screw fails in vivo.
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Unless otherwise indicated herein, the approaches described in this section are not prior art to the claims in this application and are not admitted to be prior art by inclusion in this section.
Bone screws have been used in spinal instrumentation since the 1960s to manage bone fractures and correct deformity. For example, the pedicle screw may provide a means of gripping a spinal segment, where the screw acts as a firm anchor point in one vertebra that can be connected to other such anchor points in other vertebrae with a rod. With two or more consecutive vertebrae fixated by such a construct, motion between the vertebrae is prevented, which assists in spinal fusion procedures by holding bony structures together. Many surgeons also believe that pedicle screws enhance patient recovery because they provide immediate stability for the spine and early mobilization for the patient.
SUMMARYIn accordance with one embodiment of the disclosure, a bone screw includes a shank, a threaded portion formed on an end of the shank, a frangible region formed in the shank, and an unthreaded portion disposed between the threaded portion and the frangible portion, wherein the unthreaded portion is configured to facilitate removal of the threaded portion of the screw from a bone when the frangible portion of the screw has broken after installation of the screw in the bone.
In accordance with another embodiment of the disclosure, a pedicle screw includes a shank, a threaded portion formed on an end of the shank, and an unthreaded portion disposed in a center portion of the shank, wherein the unthreaded portion is configured to facilitate removal of the threaded portion of the screw from a bone.
In accordance with a further embodiment of the disclosure, a method for treating an injury includes selecting a bone screw having a threaded portion formed on an end of a shank, a frangible region formed in the shank, and an unthreaded portion disposed between the threaded portion and the frangible portion, wherein the unthreaded portion is configured to facilitate removal of the threaded portion of the screw from the bone when the frangible portion of the screw has broken after installation of the screw in the bone, and installing the screw into a bone.
The foregoing summary is illustrative only and is not intended to be in any way limiting. In addition to the illustrative aspects, embodiments, and features described above, further aspects, embodiments, and features will become apparent by reference to the drawings and the following detailed description.
In the following detailed description, reference is made to the accompanying drawings, which form a part hereof. In the drawings, similar symbols typically identify similar components, unless context dictates otherwise. The illustrative embodiments described in the detailed description, drawings, and claims are not meant to be limiting. Other embodiments may be utilized, and other changes may be made, without departing from the spirit or scope of the subject matter presented here. It will be readily understood that the aspects of the disclosure, as generally described herein, and illustrated in the Figures, can be arranged, substituted, combined, and designed in a wide variety of different configurations, all of which are explicitly contemplated and make part of this disclosure.
While bone screws have long been used for a large number of applications, some drawbacks are known. For example, bone screws are typically left in place permanently to avoid the complications that may arise from reoperative surgery. Over time, such screws may fracture and fail, requiring removal. Because the point of failure of a bone screw is commonly in a threaded portion of the screw or at a junction between a threaded portion and an unthreaded portion of the screw, the broken screw fragment, i.e., the screw tip, can be deeply embedded in the now-healed bone material. Removal of such a screw fragment can involve enlarging the bony tunnel around the screw fragment to provide access to the fragment, possibly causing excessive loss of bone mass and/or bone fracture. Alternatively, the screw fragment may have to remain in the bone, which can be physiologically and psychologically problematic for the patient.
Embodiments disclosed herein contemplate a bone screw configured to simplify the removal of the screw in the event that the screw fails in vivo. According to some embodiments, a bone screw may be configured to fracture at a pre-selected frangible location so that the point of failure is not in an inaccessible location, e.g., deeply embedded below the surface of a treated bone. The bone screw may further include a material disposed over the frangible location that is designed to temporarily strengthen the screw and selected to be absorbed by the body over a period of time after installation of the screw in the bone. According to some embodiments, a bone screw may include an unthreaded portion that is configured to facilitate removal of an embedded screw fragment from a bone in the event that the screw fails in vivo.
Threaded portion 101 may be formed into the shank of bone screw 100 and may be substantially similar in configuration to the threaded portion of traditional pedicle screws. To wit, in some embodiments, threaded portion 101 may be self-tapping to simplify installation and/or may have a thread depth that increases toward the tip to enhance pullout strength. A length 110 and major diameter 111 of threaded portion 101 may vary depending on the size of bone into which bone screw 100 will be installed and the desired depth of placement of bone screw 100. For example, length 110 and major diameter 111 may be smaller for installation in smaller bones, such as the thoracic vertebrae, than for installation in larger bones, such as the lumbar and sacral vertebrae.
Unthreaded portion 102 may be formed into the shank of bone screw 100 adjacent to threaded portion 101 and is configured to facilitate removal of threaded portion 101 from a bone if bone screw 100 fails in vivo after installation. For example, in some embodiments, unthreaded portion 102 may include at least one pair of flat and substantially parallel sides, thereby providing gripping surfaces for unscrewing threaded portion 101 from a bone when threaded portion 101 is completely embedded in a bone. In some embodiments, as shown in
In
In other embodiments, unthreaded portion 102 may be configured to have a width or diameter that is substantially equal to major diameter 111, but larger than a minor diameter 112 of threaded portion 101, so that unthreaded portion 102 does not act as a mechanical stop against a bone during installation of bone screw 100.
Referring back to
According to some embodiments, bone screw 100 may include a material designed to temporarily strengthen bone screw 100, where the material is selected to be absorbed by the body over a period of time after installation of the screw in the bone. The absorbable material may be disposed over frangible region 103 to structurally support the portion of bone screw 100 that is weakened by the presence of frangible region 103. In such embodiments, the absorbable material reinforces bone screw 100 during the time that bony structures anchored together by one or more bone screws 100 fuse together and increase in structural strength. As the treated bony structures become stronger, bone screw 100 is slightly weakened in frangible region 103 because the absorbable material is slowly absorbed by the body of the patient. Consequently, once the treated bony structures have healed, frangible region 103 may be slightly weakened so that the failure point of bone screw 100 will be in the desired location. The one or more absorbable materials disposed over frangible region 103 may be selected based on mechanical properties, i.e., modulus of elasticity, etc., and absorbability by the human body. Example absorbable materials include calcium phosphate and calcium sulphate.
In operation, bone screw 100 may be inserted into a bony structure, such as a pedicle bone of a thoracic, sacral, or lumbar vertebra, to act as an anchor for a connecting rod and/or to hold one or more other bony structures in place as an adjunct to spinal fusion surgery.
In block 1001 (SELECT BONE SCREW), a bone screw 100 is selected having threaded portion 101 formed on an end of a shank, frangible region 103 formed in the shank, and unthreaded portion 102 disposed between threaded portion 101 and frangible portion 103. Unthreaded portion 102 may be configured to facilitate removal of threaded portion 101 from a bone when frangible portion 103 has broken after installation of bone screw 100 in a bone. For example, unthreaded portion 102 may have a hexagonal cross section configured to mate with the inner sleeve of a sleeved tool. In some embodiments, the selection of bone screw 100 may be based on a desired depth of insertion for bone screw 100 into the bone and a length of threaded portion 101.
In block 1002 (INSTALL BONE SCREW), bone screw 100 is inserted in the bone until threaded portion 101 is substantially embedded in the bone and at least a portion of unthreaded portion 102 is exposed outside the bone. In some embodiments, bone screw 100 may be inserted in the bone via a pilot hole. In some embodiments, unthreaded portion 102 may be configured to interfere with the circular opening formed in the bone by threaded portion 101, thereby acting as a mechanical stop. In such embodiments, unthreaded portion 102 may be wider than major diameter 111 of threaded portion 101.
In block 1003 (REMOVE SCREW FRAGMENT), a screw fragment is removed from the bone after bone screw 100 has undergone mechanical failure at frangible portion 103. In some embodiments, the screw fragment is removed from the bone using unthreaded portion 102. In some embodiments, a sleeved tool configured to fit the cross-section of unthreaded portion 102 may be used to unscrew the screw fragment from the bone. In some embodiments, a small amount of bone material may be removed around unthreaded portion 102 to provide more access thereto for the sleeved tool.
The foregoing detailed description has set forth various embodiments of the devices and/or processes via the use of block diagrams, flowcharts, and/or examples. Insofar as such block diagrams, flowcharts, and/or examples contain one or more functions and/or operations, it will be understood by those within the art that each function and/or operation within such block diagrams, flowcharts, or examples can be implemented, individually and/or collectively, by a wide range of hardware, software, firmware, or virtually any combination thereof.
The herein described subject matter sometimes illustrates different components contained within, or connected with, different other components. It is to be understood that such depicted architectures are merely exemplary, and that in fact many other architectures can be implemented which achieve the same functionality. In a conceptual sense, any arrangement of components to achieve the same functionality is effectively “associated” such that the desired functionality is achieved. Hence, any two components herein combined to achieve a particular functionality can be seen as “associated with” each other such that the desired functionality is achieved, irrespective of architectures or intermedial components. Likewise, any two components so associated can also be viewed as being “operably connected”, or “operably coupled”, to each other to achieve the desired functionality, and any two components capable of being so associated can also be viewed as being “operably couplable”, to each other to achieve the desired functionality. Specific examples of operably couplable include but are not limited to physically mateable and/or physically interacting components.
With respect to the use of substantially any plural and/or singular terms herein, those having skill in the art can translate from the plural to the singular and/or from the singular to the plural as is appropriate to the context and/or application. The various singular/plural permutations may be expressly set forth herein for sake of clarity.
It will be understood by those within the art that, in general, terms used herein, and especially in the appended claims (e.g., bodies of the appended claims) are generally intended as “open” terms (e.g., the term “including” should be interpreted as “including but not limited to,” the term “having” should be interpreted as “having at least,” the term “includes” should be interpreted as “includes but is not limited to,” etc.). It will be further understood by those within the art that if a specific number of an introduced claim recitation is intended, such an intent will be explicitly recited in the claim, and in the absence of such recitation no such intent is present. For example, as an aid to understanding, the following appended claims may contain usage of the introductory phrases “at least one” and “one or more” to introduce claim recitations. However, the use of such phrases should not be construed to imply that the introduction of a claim recitation by the indefinite articles “a” or “an” limits any particular claim containing such introduced claim recitation to inventions containing only one such recitation, even when the same claim includes the introductory phrases “one or more” or “at least one” and indefinite articles such as “a” or “an” (e.g., “a” and/or “an” should typically be interpreted to mean “at least one” or “one or more”); the same holds true for the use of definite articles used to introduce claim recitations. In addition, even if a specific number of an introduced claim recitation is explicitly recited, those skilled in the art will recognize that such recitation should typically be interpreted to mean at least the recited number (e.g., the bare recitation of “two recitations,” without other modifiers, typically means at least two recitations, or two or more recitations). Furthermore, in those instances where a convention analogous to “at least one of A, B, and C, etc.” is used, in general such a construction is intended in the sense one having skill in the art would understand the convention (e.g., “a system having at least one of A, B, and C” would include but not be limited to systems that have A alone, B alone, C alone, A and B together, A and C together, B and C together, and/or A, B, and C together, etc.). In those instances where a convention analogous to “at least one of A, B, or C, etc.” is used, in general such a construction is intended in the sense one having skill in the art would understand the convention (e.g., “a system having at least one of A, B, or C” would include but not be limited to systems that have A alone, B alone, C alone, A and B together, A and C together, B and C together, and/or A, B, and C together, etc.). It will be further understood by those within the art that virtually any disjunctive word and/or phrase presenting two or more alternative terms, whether in the description, claims, or drawings, should be understood to contemplate the possibilities of including one of the terms, either of the terms, or both terms. For example, the phrase “A or B” will be understood to include the possibilities of “A” or “B” or “A and B.”
While various aspects and embodiments have been disclosed herein, other aspects and embodiments will be apparent to those skilled in the art. The various aspects and embodiments disclosed herein are for purposes of illustration and are not intended to be limiting, with the true scope and spirit being indicated by the following claims.
Claims
1. A bone screw comprising:
- a shank;
- a threaded portion formed on an end of the shank;
- a frangible region formed in the shank; and
- an unthreaded portion disposed between the threaded portion and the frangible portion,
- wherein the unthreaded portion is configured to facilitate removal of the threaded portion of the screw from a bone when the frangible portion of the screw has broken after installation of the screw in the bone.
2. The bone screw of claim 1, wherein the frangible portion is a reduced-cross-section portion of the shank.
3. The bone screw of claim 2, wherein the reduced-cross-section portion is an annular groove.
4. The bone screw of claim 2, wherein the frangible region has a cross-sectional area that is at least about 10% less than the cross-sectional area of the unthreaded portion.
5. The bone screw of claim 2, further comprising a material disposed over the frangible portion, wherein the material is an absorbable material selected to be absorbable in-vivo after installation of the screw in the bone.
6. The bone screw of claim 5, wherein the material is selected from the group of absorbable materials consisting of calcium phosphate and calcium sulphate.
7. The bone screw of claim 1, wherein the unthreaded portion comprises at least one pair of flat and substantially parallel sides.
8. The bone screw of claim 7, wherein the unthreaded portion is hexagonal in cross section.
9. The bone screw of claim 1, wherein the cross section of the unthreaded portion is configured to interfere with a circular opening having a diameter equal to the major diameter of the threaded portion.
10. The bone screw of claim 1, wherein the cross-sectional area of the unthreaded portion is less than the cross-sectional area of the minor diameter of the threaded portion.
11. The bone screw of claim 5, wherein the material disposed over the frangible portion extends over the frangible portion to form a surface flush with a surface of the unthreaded portion.
12. A pedicle screw comprising:
- a shank;
- a threaded portion formed on an end of the shank; and
- an unthreaded portion disposed in a center portion of the shank,
- wherein the unthreaded portion is configured to facilitate removal of the threaded portion of the screw from a bone.
13. The pedicle screw of claim 12, further comprising a frangible region formed in the shank, wherein the frangible portion is a reduced-cross-section portion of the shank.
14. The pedicle screw of claim 13, further comprising an absorbable material disposed over the frangible region, wherein the absorbable material is selected to be absorbable in-vivo after installation of the screw in the bone.
15. A method for treating an injury, comprising:
- selecting a bone screw having a threaded portion formed on an end of a shank, a frangible region formed in the shank, and an unthreaded portion disposed between the threaded portion and the frangible portion, wherein the unthreaded portion is configured to facilitate removal of the threaded portion of the screw from the bone when the frangible portion of the screw has broken after installation of the screw in the bone; and
- installing the screw into a bone.
16. The method of claim 15, wherein the selecting is based on a desired depth of insertion for the screw into the bone and a length of the threaded portion.
17. The method of claim 15, wherein the installing comprises
- drilling a pilot hole into the bone; and
- inserting the screw into the pilot hole until the threaded portion is substantially embedded in the bone and at least a portion of the unthreaded portion is exposed outside the bone.
18. The method of claim 15, further comprising removing the threaded portion from the bone using the unthreaded portion, wherein the removing occurs after the screw has broken at the frangible region.
19. The method of claim 18, wherein the removing comprises unscrewing the threaded portion from the bone using a sleeved tool configured to fit the cross-section of the unthreaded portion.
20. The method of claim 19, wherein the unthreaded portion is hexagonal in cross-section and the removing comprises removing the threaded portion from the bone using an inner-hexagon sleeve.
Type: Application
Filed: Aug 2, 2010
Publication Date: May 23, 2013
Patent Grant number: 8753380
Applicant: TONGJI UNIVERSITY (Shanghai)
Inventors: Liming Cheng (Shanghai), Yan Yu (Shanghai), Zhili Zeng (Shanghai), Wei Xu (Shanghai), Yongwei Jia (Shanghai), Lie Qian (Shanghai), Rui Zhu (Shanghai), Jianjie Wang (Shanghai), Zhourui Wu (Shanghai)
Application Number: 13/376,440
International Classification: A61B 17/86 (20060101);